A pyrotechnic initiator converts an electrical signal into a controlled output flame. A primer generates a flash and a booster pellet converts the flash into a controlled burn that is provided at an outlet. The flame performs a function, for example ignition of a volume of solid, liquid, or gas propellant.
Current ignition systems, for example as disclosed in U.S. Pat. No. 5,588,366, are designed to ignite solid propellants. In such systems, the reaction generally results in an explosion that is difficult to precisely control, leading to variability in the outcome. When the pyrotechnic is initiated, the outlet region of the propellant chamber disintegrates under the force of the reaction, and the resulting byproducts interfere with the flame. Consequently, the ignition is generally erratic and unpredictable, and therefore burning of the propellant is difficult to control in a repeatable fashion.
With the advent of liquid and gel propellants that have the potential for a more consistent reaction, designers are finding that contemporary chemical ignition systems are inadequate for providing the level of precision required to take full advantage of the advantageous properties of the liquid and gel propellants. Liquid and gel propellants are commonly contained in a reservoir prior to combustion by the igniter in a reaction chamber. For liquid and gel propellants, the igniter performs two functions: displacement of a regenerative piston to initiate propellant injection; and generation of hot, high-pressure gas to ignite the cold liquid/gel propellant as it enters the combustion chamber. The parameters of interest are the rate of rise in pressure (i.e., mass and energy fluxes), the maximum pressure, and the duration of the igniter. Such parameters are tailored to the characteristics of the injection piston and the liquid/gel propellant reservoir, in order to ensure that the reservoir pressure is greater than the reaction chamber pressure when the injector opens. Due to their poor flame distribution, conventional initiators are inadequate for operation with liquid and gel propellants. As a result, designers resort to laser ignition technology, which is highly accurate, but, due to the complex nature of the technology, tends to be cumbersome and expensive, and therefore does not lend itself well to high-volume applications.
The present invention is directed to a high-precision pyrotechnic initiator well adapted for rapid, precise ignition of all forms of energetics, including liquid and gel energetics. A rigid housing, for example formed of stainless steel, contains a pyrotechnic in a hermetically sealed environment. The reaction of the pyrotechnic is confined to the housing. The release of energy creates a hot particulate in which the formation of solids is mitigated or eliminated. The flame is directed down a microcapillary flash tube including a primary front vent and secondary side vents, which generates a more evenly distributed flame spread, and which increases system efficiency and reliability. A redundant dual bridge wire may also be provided for improving ignition reliability. The assembly thereby performs the combined functions of both an igniter and a flash tube and a complete ignition train is provided in a manner that overcomes the limitations of the conventional configurations. High internal chamber pressure is attained, and superheated particulates are delivered through the vented flash tube, thereby creating a sustained regenerative process, while avoiding long ignition delays. The resulting system of the present invention is therefore suitable for operation with liquid and gel propellants.
A tube, referred to as a flash tube, can be mounted to the outlet for directing the flame, and side vents can be provided on the flash tube for generating a more evenly distributed flame spread about the flash tube.
In one aspect, the present invention is directed to a pyrotechnic initiator. The initiator includes a housing having an inner chamber and an outlet. A pyrotechnic charge is located within the chamber. The housing is of sufficient mechanical integrity to withstand internal pressure of the pyrotechnic charge when activated, such that the internal pressure is released at the outlet.
The pyrotechnic initiator may further comprise a vent tube in communication with the outlet having a longitudinal primary vent for directing activated pyrotechnic charge from the inner chamber through an entrance aperture of the primary vent to an exit aperture. The pyrotechnic initiator may further include lateral secondary side vents in communication with the longitudinal primary vent for directing activated pyrotechnic charge to the side of the vent tube.
A groove may be formed in an outer surface of the vent tube, and an O-ring positioned in the groove, for providing a barrier to escape of initiated pyrotechnic charge between the outer surface of the vent tube and the outlet. The O-ring preferably deforms upon activation of the pyrotechnic charge to seal a gap between the outer surface of the vent tube and the outlet. The width of the O-ring is preferably less than that of the groove to allow for equal distribution of pressure from the initiated charge across a side surface of the O-ring.
The O-ring may comprise first, second and third sub-O-rings positioned adjacent each other in the groove. The first and third sub-O-rings are positioned on opposite sides of the second O-ring, in which case the first and third sub-O-rings comprise Bakelite and wherein the second O-ring comprises Neoprene.
A bridge wire is included for conducting current to initiate activation of the pyrotechnic charge. In one example the bridge wire comprises first and second redundant bridge wires that may be configured in a cross pattern for distribution of the current through the pyrotechnic charge. First and second contact pins pass through the housing and are electrically coupled to corresponding first and second portions of the bridge wire for delivering current to the bridge wires. A pin seal is provided along at least a portion of the bodies of the first and second pins for sealing the interface between the first and second pins and the housing.
A first moisture barrier may be provided at the entrance aperture of the primary vent, for example comprising a fluoropolymeric seal. A retention sleeve, for example comprising nylon, may be provided in the chamber between the pyrotechnic charge and the vent tube for securing the vent tube in the outlet.
The pyrotechnic charge may comprise a material selected from the group of materials consisting of: cis-bis-(5-nitrotetrazolato)tetraminecobalt(III)perchlorate (BNCP), zirconium potassium perchlorate (ZPP), titanium-hydride-potassium-perchlorate (THPP), and lead azide (PbN6).
The housing preferably comprises stainless steel of sufficient structural integrity and/or composition so as to contain the energy released by the pyrotechnic charge when activated. The housing may comprise a plurality of body portions that are welded together to form the housing.